Question: Solve for $x$ and $y$ using substitution. ${-4x-y = 12}$ ${y = 4x-4}$
Explanation: Since $y$ has already been solved for, substitute $4x-4$ for $y$ in the first equation. ${-4x - }{(4x-4)}{= 12}$ Simplify and solve for $x$ $-4x-4x + 4 = 12$ $-8x+4 = 12$ $-8x+4{-4} = 12{-4}$ $-8x = 8$ $\dfrac{-8x}{{-8}} = \dfrac{8}{{-8}}$ ${x = -1}$ Now that you know ${x = -1}$ , plug it back into $\thinspace {y = 4x-4}\thinspace$ to find $y$ ${y = 4}{(-1)}{ - 4}$ $y = -4 - 4$ $y = -8$ You can also plug ${x = -1}$ into $\thinspace {-4x-y = 12}\thinspace$ and get the same answer for $y$ : ${-4}{(-1)}{ - y = 12}$ ${y = -8}$